A tubing string is commonly used to collect oil from a below-surface reservoir. The tubing string is conventionally constructed in threaded sections. With low-pressure reservoirs, a pump will be installed in-line in the tubing string to force the oil upwardly to the surface. A common pump configuration has a stator threaded into the tubing string and an internal spiral-like rotor oriented with the direction of the tubing string. The forces required to rotate the rotor in one angular direction to pump oil to the surface are reacted in an opposite direction through the stator into the tubing string. This tends to rotate the tubing string, which is undesirable.
An anchoring device for preventing such rotation of a tubing string is commercially available and described in U.S. Pat. No. 4,901,793 to Weber. The device has an outer cylindrical housing and an inner mandrel, which rotate relative to one another. Upper and lower ends of the mandrel are threaded in a standard manner into the tubing string. Four spring-biased drags extend from the housing to anchor it to the stationary well casing. Displaceable slips are located within the housing. A mechanical linkage internal to the housing displaces the slips to and from the well casing in response to rotation of the mandrel. To engage the slips with the well casing, the entire tubing string may be appropriately rotated in a particular angular direction from the surface. To disengage the slips, the tubing string is rotated in an opposite direction. The slips lock to the well casing when the tubing string rotates in the same direction that the associated pump. The prior device has on at least one occasion failed to disengage from the well casing. To release the device, components in the mechanical linkage apparently had to be sheared, and a drag was apparently lost.
The present invention provides a simple and reliable device for anchoring a tubing string to a well casing. At least in preferred form, the anchoring device can readily disengage from the well casing and is less subject to damage.